High Total Acid Number (TAN) crudes are discounted by about $0.50/TAN/BBL. The downstream business driver to develop technologies for TAN reduction is the ability to refine low cost crudes. The upstream driver is to enhance the market value of high-TAN crudes.
The current approach to refine acidic crudes is to blend the acidic crudes with non acidic crudes so that the TAN of the blend is no higher than about 0.5. Most major oil companies use this approach. The drawback with this approach is that it limits the amount of acidic crude that can be processed. Additionally, it is known in the art to treat the crudes with inorganic bases such as potassium and sodium hydroxide to neutralize the acids. This approach, however, forms emulsions which are very difficult to break and, additionally, undesirably leaves potassium or sodium in the treated crude. Furthermore, such prior art techniques are limited by the molecular weight range of the acids they are capable of removing.
With the projected increase of acidic crudes in the market (Chad, Venezuela, North Sea) new technologies are needed to further refine higher TAN crudes and crude blends. Thermal treatment, slurry hydroprocessing and calcium neutralization are some of the promising approaches that have emerged. However, these technologies do not extract the acids from the crudes. Instead, they convert the acids to products that remain in the crude.
U.S. Pat. No. 4,752,381 is directed to a method for neutralizing the organic acidity in petroleum and petroleum fractions to produce a neutralization number of less than 1.0. The method involves treating the petroleum fraction with a monoethanolamine to form an amine salt followed by heating for a time and at a temperature sufficient to form an amide. Such amines will not afford the results desired in the instant invention since they convert the naphthenic acids, whereas the instant invention extracts and removes them.
U.S. Pat. No. 2,424,158 is directed to a method for removing organic acids from crude oils. The patent utilizes a contact agent which is an organic liquid. Suitable amines disclosed are mono-, di-, and triethanolamine, as well as methyl amine, ethylamine, n- and isopropyl amine, n-butyl amine, sec-butyl amine, ter-butyl amine, propanol amine, isopropanol amine, butanol amine, sec-butanol, sec-butanol amine, and ter-butanol amine. Such amines have been found to be ineffective in applicants' invention.